1. Field of the Invention
The present invention relates to a positioning element for holding a charge couple device (CCD) in an optical scanner where the optical alignment of the CCD to the position of the document's image can be easily made in the assembly process without further adjustment.
2. Description of Related Art
In an optical scanner, the image of a scanned document is reflected by some mirrors, focused by a lens and imaged on a CCD, and then transformed into digital signals for processing by computers. In recent manufacturing processes, the assembly of the lens and the CCD has been incorporated into a module in which the lens and the CCD have to be adjusted and aligned into suitable optical positions in order to take sharp image from the document.
Two alignment methods of prior arts are as follows:
1) Electronic Method
As shown in FIG. 1A, an alignment arrangement for an optical scanner includes a sample scale 10, a light source 12, four reflection mirrors 14, a lens 16, and a CCD 18 mounted on a printed circuit board 24. The arrangement corrects the alignment by checking the electronic wave of the scanning signals being transformed from the image of the scale 10 by the CCD 18, and adjusting the position of the CCD 18 relative to the lens 16. In this way, the sample scale 10 is fixed, and the CCD 18 is to be adjusted.
2) Optical Method
As shown in FIG. 1B, an alignment arrangement for an optical scanner includes the same components of FIG. 1A: a sample scale 10, a light source 12, four reflection mirrors 14, a lens 16, and a CCD 18 mounted on a printed circuit board 24. The module of lens 16 and CCD 18 is first settled by using an optical instrument, such as a microscope, to adjust the position of the CCD 18 relative to the lens 16 for a correct focusing. In this way, the CCD 18 and the lens 16 are off-line adjusted.
No matter what method is utilized, the positioning of the CCD 18 has to be provided with in three degrees of freedom as illustrated in FIG. 2.
FIG. 2 shows a composition of a conventional lens and CCD module and its alignment requirement. Firstly, a lens 16 mounted in a holder 20 on an axes 22 is adjustable by using a driver 23 to move inwards or outwards for focusing on a CCD 18. Since the CCD 18 has been soldered on a PCB (printed circuit board) 24, we have to adjust the PCB 24 in movements of X-direction, Z-direction and Y-rotation as illustrated in order to align a scanned image on the optoelectronic elements 47 before fastening the PCB 24 to the holder 20 with two screws 28 movable in two slots 26. Because the adjustment has to be done in aforesaid three degrees of freedom, it is complicated, time consuming and eventually difficult to achieve a reliable alignment.